Association of Rare <i>APOE</i> Missense Variants V236E and R251G With Risk of Alzheimer Disease
Authors: Yann Le Guen, Michael E. Belloy, Benjamin Grenier-Boley, Itziar de Rojas, Atahualpa Castillo-Morales, Iris Jansen, Aude Nicolas, Céline Bellenguez, Carolina Dalmasso, Fahri Küçükali, Sarah J. Eger, Katrine Laura Rasmussen, Jesper Qvist Thomassen, Jean-François Deleuze, Zihuai He, Valerio Napolioni, Philippe Amouyel, Frank Jessen, Patrick G. Kehoe, Cornelia van Duijn, Magda Tsolaki, Pascual Sánchez-Juan, Kristel Sleegers, Martin Ingelsson, Giacomina Rossi, Mikko Hiltunen, Rebecca Sims, Wiesje M. van der Flier, Alfredo Ramirez, Ole A. Andreassen, Ruth Frikke-Schmidt, Julie Williams, Agustín Ruiz, Jean-Charles Lambert, Michael D. Greicius, Beatrice Arosio, Luisa Benussi, Anne Boland, Barbara Borroni, Paolo Caffarra, Delphine Daian, Antonio Daniele, Stéphanie Debette, Carole Dufouil, Emrah Düzel, Daniela Galimberti, Vilmantas Giedraitis, Timo Grimmer, Caroline Graff, Edna Grünblatt, Olivier Hanon, Lucrezia Hausner, Stefanie Heilmann-Heimbach, Henne Holstege, Jakub Hort, Deckert Jürgen, Teemu Kuulasmaa, Aad van der Lugt, Carlo Masullo, Patrizia Mecocci, Shima Mehrabian, Alexandre de Mendonça, Susanne Moebus, Benedetta Nacmias, Gael Nicolas, Robert Olaso, Goran Papenberg, Lucilla Parnetti, Florence Pasquier, Oliver Peters, Yolande A. L. Pijnenburg, Julius Popp, Innocenzo Rainero, Inez Ramakers, Steffi Riedel-Heller, Nikolaos Scarmeas, Philip Scheltens, Norbert Scherbaum, Anja Schneider, Davide Seripa, Hilkka Soininen, Vincenzo Solfrizzi, Gianfranco Spalletta, Alessio Squassina, John van Swieten, Thomas J. Tegos, Lucio Tremolizzo, Frans Verhey, Martin Vyhnalek, Jens Wiltfang, Mercè Boada, Pablo García-González, Raquel Puerta, Luis M. Real, Victoria Álvarez, María J. Bullido, Jordi Clarimon, José María García-Alberca, Pablo Mir, Fermin Moreno, Pau Pastor, Gerard Piñol-Ripoll, Laura Molina-Porcel, Jordi Pérez-Tur, Eloy Rodríguez-Rodríguez, Jose Luís Royo, Raquel Sánchez-Valle, Martin Dichgans, Dan Rujescu
Journal: JAMA Neurology (2022)

The APOE ε2 and APOE ε4 alleles are the strongest protective and risk-increasing, respectively, genetic variants for late-onset Alzheimer disease (AD). However, the mechanisms linking APOE to AD-particularly the apoE protein's role in AD pathogenesis and how this is affected by APOE variants-remain poorly understood. Identifying missense variants in addition to APOE ε2 and APOE ε4 could provide critical new insights, but given the low frequency of additional missense variants, AD genetic cohorts have previously been too small to interrogate this question robustly.To determine whether rare missense variants on APOE are associated with AD risk.Association with case-control status was tested in a sequenced discovery sample (stage 1) and followed up in several microarray imputed cohorts as well as the UK Biobank whole-exome sequencing resource using a proxy-AD phenotype (stages 2 and 3). This study combined case-control, family-based, population-based, and longitudinal AD-related cohorts that recruited referred and volunteer participants. Stage 1 included 37 409 nonunique participants of European or admixed European ancestry, with 11 868 individuals with AD and 11 934 controls passing analysis inclusion criteria. In stages 2 and 3, 475 473 participants were considered across 8 cohorts, of which 84 513 individuals with AD and proxy-AD and 328 372 controls passed inclusion criteria. Selection criteria were cohort specific, and this study was performed a posteriori on individuals who were genotyped. Among the available genotypes, 76 195 were excluded. All data were retrieved between September 2015 and November 2021 and analyzed between April and November 2021.In primary analyses, the AD risk associated with each missense variant was estimated, as appropriate, with either linear mixed-model regression or logistic regression. In secondary analyses, associations were estimated with age at onset using linear mixed-model regression and risk of conversion to AD using competing-risk regression.A total of 544 384 participants were analyzed in the primary case-control analysis; 312 476 (57.4%) were female, and the mean (SD; range) age was 64.9 (15.2; 40-110) years. Two missense variants were associated with a 2-fold to 3-fold decreased AD risk: APOE ε4 (R251G) (odds ratio, 0.44; 95% CI, 0.33-0.59; P = 4.7 × 10-8) and APOE ε3 (V236E) (odds ratio, 0.37; 95% CI, 0.25-0.56; P = 1.9 × 10-6). Additionally, the cumulative incidence of AD in carriers of these variants was found to grow more slowly with age compared with noncarriers.In this genetic association study, a novel variant associated with AD was identified: R251G always coinherited with ε4 on the APOE gene, which mitigates the ε4-associated AD risk. The protective effect of the V236E variant, which is always coinherited with ε3 on the APOE gene, was also confirmed. The location of these variants confirms that the carboxyl-terminal portion of apoE plays an important role in AD pathogenesis. The large risk reductions reported here suggest that protein chemistry and functional assays of these variants should be pursued, as they have the potential to guide drug development targeting APOE.